Thats BS. Most anyone who liked SS 5 years ago are still back for most every update or two. The game is still as popular as ever albeit people are just triggered at having to wait so long for the more trademark character themed big updates as its of course been a while. As for longetivity popular games still remain popular - DMD, Harem Hotel, Glassix, Corruption, Love and Second Base etc. Theyre ALL still going. Some are stuck in quandry for trying to update their games like this one sure, Ecchi Sensei comes to mind of the absolute laughable disaster that can come from incompetent attempts at it (thankfully this dev team far better at what they do).
What do you ask them to do? End SS and start a second project? How will that work out and how many have pulled a big hit into a second one? Not the devs of Dating My Daughter, Parental Love or Dark Neighbourhood. People are even citing burnout from Treasure of Nadia on its devs newest project as three games in people are finding its formular too familiar (signature style is signature style - they can accept it on established games but on new games its just more of the same but different characters). There will be rare exeptions to every rule certainly (Doctor PinkCake comes to mind) but most do NOT want the games to end and new ones to take their place. Milfy City was already given as an example, the likes of Dark Magic devs have had similar backlash for looking into an alternate project instead of focusing on the main one and the likes of Alorath is constantly called lazy over small or slow updates completely overlooking hes usually working on about four different games at once.
Ill summarize with an old chestnut - "if it aint broke, dont fix it". The girls in the planned proper updates once they start rolling out were voted for, the demand is there. We just need to get to them.